The genetic overlap between Alzheimer's disease, amyotrophic lateral sclerosis, Lewy body dementia, and Parkinson's disease

Neurodegenerative diseases are a group of disorders characterised by neuronal cell death causing a variety of physical and mental problems. While these disorders can be characterised by their phenotypic presentation within the nervous system, their aetiologies differ to varying degrees. Some disorders, such as Lewy body dementia and Parkinsons disease, show overlap in the major proteins found in aggregates, and some diseases, like Alzheimers disease, amyotrophic lateral sclerosis, and Parkinsons disease, are influenced by the same non-neuronal cell types (microglia), suggesting partly shared aetiologies. The identification of shared genetic risk factors common to many neurodegenerative diseases may highlight fundamental biological processes involved in neurodegeneration and provide promising targets for treatment and drug repurposing. The majority of genetic evidence for overlap between neurodegenerative diseases has been pairwise, with little genetic evidence for genes or biological processes found across more than two neurodegenerative diseases. In this study, we aimed to identify overlap between the four investigated neurodegenerative disorders (Alzheimers disease, amyotrophic lateral sclerosis, Lewy body dementia, and Parkinsons disease) at the variant, gene, genomic locus, gene-set, cell, or tissue level, with specific interest in overlap between three or more diseases. Using local genetic correlation, we found that the TMEM175 locus was a shared locus between amyotrophic lateral sclerosis, Lewy body dementia, and Parkinsons disease, and the HLA region was shared between Alzheimers disease, amyotrophic lateral sclerosis, and Parkinsons disease. We also highlighted genes, genomic loci, gene-sets, cell types, and tissue types which may be important to two or more disorders by analysing the association of variants with a common factor estimated from the four disorders. Our study successfully highlighted genetic loci and tissues associated with two or more neurodegenerative diseases.